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Discussion Starter · #1 ·
I've noticed that my 2000 1.4 145 normally idles at about 900 rpm but occasionally it revs itself up to about 1500 and then settles down again.

Yesterday I was stuck at a set of traffic and it went from 900 to nearly 2000 a couple of times (3/4) in a row and then it settled down. (The other drivers around me probably thought I as looking got a race
)

Is this normal? I know TC has experienced something similar with his 1.8 145.
 

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I get this on my Q4 when starting from cold. I usually let it idle for 3-4 mins before setting off, during which time the car happily sits there reving between 800-2000 rpm, It then sits at 2000 rpm for a minute of so before returning to normal. I think I've got a dirty throttle position sensor (TPS) but because it only happens at startup from cold I can't be bothered fixing it. My guess would be that you have the same problem, although being a 2000 car, your TPS seems to have picked up dirt very quickly.

Steve
 

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Ben answered the same question on another forum...
which I stumbled across

Read on


Sounds like there is a vacuum leak in your intake system.

The brake servo takes vacuum from the inlet manifold to increase braking efficiency. The idle system should compensate for this but in your case it sounds like its over, then under compensating.

A simple check of the pipes and connections should reveal something, and is best done while the motor is running and someone is pumping the brake pedal.

Dont know what year your car is but I suspect it is a T-Spark motor which has a reasonably complex idle circuit so if the problem is here it's best left to a mechanic to sort.
_________________
Later
BeCos
 

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Discussion Starter · #4 ·
I dropped by 145 into the dealer last Thursday for them to sort this problem out, they reset the parametrics on the examiner as the setting were out. But within a couple of miles of the dealers it was back at it again.....

I brought the car back in again yesterday and they replaced the stepper motor. Having driven the car for a good bit last night and again this morning it's behaving itself perfectly.....

...I'm one happy Alfa owner once again
 
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On my 155 there is a stepper motor on top of the throttle body. This looks to control the airflow into the engine when the throttle is closed by opening a rotary valve(there is a hose that connects the between the engine side of the airflow meter, the engine breather, and this valve). From experimenting with this valve I have found that disconnecting the connector causes the idle speed to go up to about 1500rpm. And on occasions my car also sticks at 1500rpm (sometimes 2000rpm if the engine is cold) I also think that this component is faulty on my car. When coming on and off the throttle sometimes the car seems to miss fire. I am sure it is not the Lambda probe as this is giving correct readings when I attach a mutimeter to the connector (plus I replaced it only 3 months ago) I need to get a replacement part to test my theory that the airflow valve is the problem, but I don't want to pay alfa prices for it.... Anybody know a good cheap Bosch agent?

Cheers

James
 

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Discussion Starter · #7 ·
Thanks for the info JamesM. I have to confess I wasn't entirely sure what the stepper motor was for. My guess was that it had something to do with the variable timing in the engine but it was only a guess. The dealers weren't too helpful in explaining what was done, I think they subscribe to the 'The owner only knows how to drive the car' philosphy and weren't going to bother explaining what they did....

Alfaowner - My alfa is a 2000 145 1.4 TS
 

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James can you advise on what reading you expect to get from a good and a bad senor reading.

Cheers!
 
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Hi there Alfaowner,

On starting the engine the lambda value should be high (say 0.6-0.7 Volts) then should decrease as the engine warms up to about 0.3 volts, then the engine should go into emission control mode.

At this point would expect the lambda voltage to vary between 0.1 and 0.9 Volts switching at a fairly regular interval - probably 10 to 15 times in 10 seconds - you need a fairly good multimeter to capture the variances (Even better with a digital scope)

This lambda action can be seen on a deal computer in the "integrator" screen. This should vary up and down with the mixture setting adjusting to compensate for the lambda reading. When My lambda probe was non functional, this reading was off the top of the scale!!

On the 155, the lambda sensor connector is under a cover on the bulkhead behind the inlet manifold. There should be a 4way Amp connector with 2 wires the same colour (these are for the heater) and 2 others. These are the 0v reference and the return from the sensor. You should be able to push the multimeter probes into the back of the connector to make sufficient contact to read the values coming from the lambda sensor.

Hope this is OK, I can find out more accurate info if required

Cheers

James
 

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Well put it this way im my MOT it states my CO should be 0.30 but mine is sitting on 7.8 !! Its very juicy right now and the cat seems to smell like bad eggs all the time, even if driven like a granny?

I will check this out at the weekend.

Many thanks
 
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